I think this is a very good shot, especially taken through glass. The detail around the eyes is excellent, as is the exposure, which is easy to mis-judge on a dark subject like this. I have a couple of suggestions for possible improvements.
I don't think the aperture of f/2.8 has given quite enough depth of field since, while the eyes are pin-sharp, the lips are a little blurry. Since the lips are a key area in this photograph, it would be better to have them sharper. That said, you were already at a high ISO setting and maybe you weren't able to use a slower shutter, in which case it may be that you opted for the best compromise. Sometimes, the only way to get that perfect shot is to come back on another day.
I think the composition could be improved a little. Eye-contact from the gorilla would make for an extremely strong shot but that doesn't help if he's looking the `wrong' way at the crucial moment. When a person or animal isn't making eye contact with us, we have a natural desire to follow their gaze to see what they're looking at. For that reason, it's usually better to place the person or animal so that they're looking `through', rather than `out of' the frame. In this case, the gorilla is on the right of the frame, looking to our right so, when we follow his gaze, we fall out of the photograph. If you'd placed him towards the left of the frame, following his eyes would naturally guide us through the shot.

I think this is a very good shot, especially taken through glass. The detail around the eyes is excellent, as is the exposure, which is easy to mis-judge on a dark subject like this. I have a couple of suggestions for possible improvements.

I don't think the aperture of f/2.8 has given quite enough depth of field since, while the eyes are pin-sharp, the lips are a little blurry. Since the lips are a key area in this photograph, it would be better to have them sharper. That said, you were already at a high ISO setting and maybe you weren't able to use a slower shutter, in which case it may be that you opted for the best compromise. Sometimes, the only way to get that perfect shot is to come back on another day.

I think the composition could be improved a little. Eye-contact from the gorilla would make for an extremely strong shot but that doesn't help if he's looking the `wrong' way at the crucial moment. When a person or animal isn't making eye contact with us, we have a natural desire to follow their gaze to see what they're looking at. For that reason, it's usually better to place the person or animal so that they're looking `through', rather than `out of' the frame. In this case, the gorilla is on the right of the frame, looking to our right so, when we follow his gaze, we fall out of the photograph. If you'd placed him towards the left of the frame, following his eyes would naturally guide us through the shot.